Bike Gear Ratio Calculator
Work out a bicycle gear ratio from the chainring and cog, and with your wheel size, gear inches, development per pedal turn and speed at a cadence.
Result
Gear ratio: 2.941
Turns of the rear wheel for each turn of the pedals.The wheel is your own measurement. A tyre’s printed size is a name rather than a measurement, so measure it or roll it out.
https://calcgallery.com/fitness-training/bike-gear-ratio-calculator/
How to use the Bike Gear Ratio Calculator
- Count the teeth on the chainring you are using at the front and the cog at the back, or read the numbers stamped on them.
- For gear inches and development, measure the wheel across the inflated tyre, or roll the bike one full wheel turn and measure how far it went.
- Add a cadence under more options to see the road speed that gear gives at that pedalling rate.
From teeth to distance
The chain moves the same number of teeth past the chainring and the cog, so each pedal turn turns the cog, and the back wheel with it, chainring teeth ÷ cog teeth times. Everything else follows from the wheel:
gear ratio = chainring teeth ÷ cog teethgear inches = gear ratio × wheel diameterdevelopment = gear ratio × wheel circumferencespeed = development × cadenceThese are the definitions Sheldon Brown sets out in his article on gain ratios. The ratio needs no measurement at all, so the page gives it on its own when no wheel is entered.
Comparing gears
Two bikes with the same chainring and cog can feel very different if their wheels differ in size. Gear inches and development include the wheel, so they compare gears across bikes. Two gear combinations with the same ratio give the same effort per pedal turn on the same bike, which is how duplicate gears in a set can be spotted.
Crank length changes how hard a gear feels as well, since a longer crank gives more leverage. Sheldon Brown’s gain ratio accounts for that; this page stays with the more common gear inches and development. For the time a ride takes at a given speed, the speed, distance and time calculator finishes the job.
With your numbers
- 50 ÷ 17 = 2.941
- Gear inches = 2.941 × 27 in = 79.4 in
- Gear ratio = 2.941
Quick reference
The wheel is your own measurement. A tyre’s printed size is a name rather than a measurement, so measure it or roll it out.
| Example | Gear ratio |
|---|---|
| 50/17 on a 27 in wheel | 2.941 |
| 34/28, 2105 mm rollout, 80 rpm | 1.214 |
| 39/21 on a 686 mm wheel | 1.857 |
| 44/16, ratio only | 2.75 |
| 50/11 at 90 rpm, 27 in wheel | 4.545 |
| 32/32 climbing gear, 27 in wheel | 1 |
Common questions about the Bike Gear Ratio Calculator
- How do I work out a bike gear ratio?
- Divide the chainring teeth by the cog teeth. A 50-tooth chainring with a 17-tooth cog is 50 ÷ 17 = 2.94, so the back wheel turns 2.94 times for each turn of the pedals. A bigger ratio is a harder, faster gear.
- What are gear inches?
- The gear ratio multiplied by the wheel diameter in inches. It is the diameter of a wheel that, driven directly by the pedals with no gearing, would travel as far per pedal turn. It lets gears on bikes with different wheel sizes be compared.
- What is development?
- The distance the bike moves for one full turn of the pedals: the gear ratio times the wheel’s circumference. It is the same comparison as gear inches, multiplied by π and usually given in metres.
- How do I measure my wheel?
- A direct way is a rollout: mark the tyre where it touches the floor, roll the bike forward one full turn with your weight on it, and measure the distance. That is the circumference. A tyre’s printed size is a naming convention rather than a measurement, so it is only a rough guide.
- How fast will I go in a gear?
- Development times cadence. At 90 pedal turns a minute, a gear with 6.34 m of development moves the bike 570 m a minute, about 34 km/h. The page assumes the tyre does not slip and ignores everything else, so it is the speed that gear and cadence produce, not a prediction for a ride.